Bicycle rear suspension system

ABSTRACT

A bicycle rear suspension linkage system comprising a bicycle frame having an upper link pivotally connected thereto. Also pivotally connected to the bicycle frame are the front ends of a pair of chain stay members, while pivotally connected to the upper link are the upper ends of a pair of seat stay members. The lower ends of the seat stay members are also pivotally connected to the back ends of the chain stay members. The rear suspension linkage system further comprises a shock absorber having a body portion and a reciprocally movable piston rod extending axially from the body portion. The piston rod defines a distal end which is pivotally connected to the seat stay members, with the body portion being pivotally connected to the upper link.

FIELD OF THE INVENTION

The present invention relates generally to bicycles, and moreparticularly to a rear suspension system for a bicycle frame whichpossesses shock absorbing characteristics and is adapted to enhance theperformance of the bicycle.

BACKGROUND OF THE INVENTION

The primary structural component of a bicycle is the bicycle frame.Typically, the bicycle frame comprises an elongate top tube which isrigidly secured to and extends between a head tube of the bicycle and aseat tube of the bicycle. The head tube typically provides a structuralbase for the stem of the bicycle to which the handle bars are attached.The seat tube provides a base for a seat post which is generallytelescopically received therewithin and to which is secured the saddleor seat of the bicycle. In typical bicycle frame construction, the seattube includes a generally cylindrical axle-receiving bracket attached tothe lower end thereof which is adapted to receive the bottom bracketaxle. The bottom bracket axle typically extends between andinterconnects the cranks to which are attached the pedals. Rigidlysecured to and extending between the head tube and the cylindricalaxle-receiving bracket is an elongate down tube.

In addition to the aforementioned structural components, rigidly securedto and extending rearwardly from the axle-receiving bracket are firstand second chain stay members. Additionally, rigidly secured to andextending downwardly from the upper end of the seat tube are first andsecond seat stay members having lower ends which are rigidly secured tothe back ends of the first and second chain stay members. Typically, thelower ends of the seat stay members and back ends of the chain staymembers are interconnected in a manner adapted to receive the rear tireaxle of the rear wheel. The head tube, seat tube, top tube and down tubeare typically secured to each other and to the axle-receiving bracket ina manner defining a main front triangle portion of the bicycle frame.The seat stay and chain stay members, when connected to the seat tube,axle-receiving bracket and each other, typically define a back triangleportion of the bicycle frame.

The foregoing description generally represents the construction ofconventional prior art bicycle frames. Typically, when such prior artframes are constructed, the aforementioned structural components arerigidly secured to one another through the use of welding or brazingtechniques. Though this method of constructing the bicycle frameprovides the resulting frame with structural integrity, the bicycleframe does not possess a suspension having shock absorbingcharacteristics. As will be recognized, the ride, comfort andperformance of the bicycle would be greatly enhanced if the bicycleframe were adapted to at least partially accommodate the shocksroutinely encountered while riding the bicycle.

Though recent prior art bicycle frames include front and/or rear shockabsorbing assemblies, such bicycle frames possess certain deficiencieswhich detract from their overall utility. In most prior art rear shockabsorbing assemblies, the rear axle pivots about a single elevated pivotpoint when subjected to a shock force which generally results in therear wheel axle moving upwardly in an arc rather than moving verticallyupward in a substantially linear fashion.

Typically, if the rear wheel axle is caused to move arcuately due to theabsorption of a bump or shock force by the rear tire, the bicycle framewill normally rise and fall a few times due to suspension oscillationsafter the obstacle or obstruction has been cleared by the rear tire.This bouncing action which occurs at a frequency attendant to thestructure of the rear shock absorbing assembly will typically requirethe rear tire to speed up and slow down as it keeps up with thebicycle's constant velocity, since the wheel base of the bicycle ischanging as the rear wheel axle moves arcuately back to its originalposition. This constant changing of the rear tire's angular velocityrequires energy due to the effects on the rear tire's angular momentum,thus diminishing riding efficiency.

Further, the rear shock absorbing assemblies are typically mounteddirectly to the main front triangle portion of the bicycle frame, andare configured in a manner which results in the amount of rear wheeltravel being greater or less than the amount of shock absorber travelwhen a shock force is applied to the rear wheel. In certain prior artrear shock-absorbing assemblies, less and less additional force isrequired to compress the shock absorber of the assembly for each equalincrement in rear wheel movement due to the mechanical advantage of theshock absorber over the rear wheel decreasing throughout the rear wheeltravel. This type of suspension wherein the wheel rate is regressive isgenerally undesirable due to the tendency of the shock absorber to"bottom-out". Other prior art rear shock absorbing assemblies areconfigured in a manner so as to achieve a progressive wheel rate whereinmore and more additional force is needed to compress the shock absorberfor each equal increment in rear wheel movement. Though a progressivewheel rate is more desirable than a regressive wheel rate, optimalperformance of the bicycle is achieved with a flat wheel rate whereinboth the shock absorber of the rear shock absorbing assembly has theadvantages attendant to a flat rear wheel rate wherein the ratio ofmovement, i.e. the motion ratio, between the shock absorber and the rearwheel is constant throughout the range of vertical travel of the rearwheel.

In addition to the foregoing, the mounting of the shock absorberassembly to the main front triangle portion of the bicycle framesometimes results in the force of the shock being transmitted directlyto the main front triangle portion of the bicycle frame as bendingmoments or torque which adversely affects the overall smoothness of thebicycle ride. As such, a much more smooth and even ride would beobtained if the shock absorber assembly was not mounted directly to themain front triangle portion of the bicycle frame, and was configured toprovide a flat rate of rear wheel travel. The present inventionspecifically overcomes these and other deficiencies associated with theprior art shock absorbing bicycle frames.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention,there is provided a shock-absorbing bicycle rear suspension linkagesystem which is adapted to provide the bicycle frame and hence thebicycle with enhanced riding comfort and performance. The bicycle rearsuspension linkage system generally comprises a bicycle frame having anupper link pivotally connected thereto. Pivotally connected to the upperlink are the upper ends of a pair of seat stay members, while pivotallyconnected to the bicycle frame are the front ends of a pair of chainstay members. The back ends of the chain stay members are themselvespivotally connected to the lower ends of the seat stay members.

The linkage system further comprises a shock absorber having a bodyportion and a reciprocally movable piston rod extending axially from thebody portion which facilitates viscous damping control when working in ahydraulic fluid. The piston rod defines a distal end which is pivotallyconnected to the seat stay members, with the body portion beingpivotally connected to the upper link. The shock absorber furthercomprises a spring member which extends between the body portion and theseat stay members, with the piston rod extending axially through thespring member.

In the preferred embodiment, the bicycle frame comprises a head tubedisposed at the front of the bicycle frame, a seat tube disposed at therear of the bicycle frame, and an elongate top tube having opposed endsrigidly attached to the head tube and the seat tube. A pair of rearwheel axle receiving members are rigidly attached to the lower ends ofthe seat stay members, and pivotally connected to the back ends of thechain stay members. Rigidly attached to the seat tube and the top tubeis a link mount to which the upper link is pivotally connected.Additionally, rigidly attached to the front ends of the chain staymembers is a chain stay end housing which is pivotally connected to theseat tube, while rigidly attached to the upper ends of the seat staymembers is a seat stay end housing which is pivotally connected to theupper link.

BRIEF DESCRIPTION OF THE DRAWINGS

These as well as other features of the present invention will becomemore apparent upon reference to the drawings wherein:

FIG. 1 is a perspective view of a bicycle incorporating the rearsuspension linkage system constructed in accordance with the presentinvention;

FIG. 2 is a partial perspective view of a portion of the rear suspensionlinkage system of the present invention;

FIG. 3 is an enlarged perspective view taken along line 3--3 of FIG. 2;

FIG. 4 is a perspective view of the shock absorber shown in FIGS. 2 and3;

FIG. 5 is a side-elevational view of the rear suspension linkage systemin the unactuated state; and

FIG. 6 is a side elevational view of the rear suspension linkage systemin the actuated state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for purposes ofillustrating a preferred embodiment of the present invention only, andnot for purposes of limiting the same, FIG. 1 perspectively illustratesa bicycle 10 incorporating a bicycle frame 12 constructed to incorporatethe bicycle rear suspension linkage system of the present invention. Thebicycle frame 12 generally comprises a head tube 14 disposed at thefront end of the bicycle 10 and a seat tube 16 disposed toward the rearend of the bicycle 10. Connected to the top end of the head tube 14 is astem 18 to which is attached the handle bars 20. Connected to the bottomend of the stem 18 is a conventional front shock absorber assembly 22defining a first fork 24 and a second fork 26 between which is mountedthe axle 28 of the front wheel 30. Importantly, the front shock absorberassembly 22 is adapted to provide the compressive first fork 24 andcompressive second fork 26 with shock absorbing capability.Telescopically received into the top end of the seat tube 16 is a seatpost 32 having a saddle or seat 34 connected thereto.

Rigidly attached to and extending between the head tube 14 and seat tube16 is an elongate top tube 36. Additionally, rigidly attached to thebottom end of the seat tube 16 is an axle receiving bracket 38 having anaxle-receiving bore 40 extending axially therethrough. In the preferredembodiment, the axle receiving bracket 38 has a generally cylindricalconfiguration and is attached to the lower end of the seat tube 16 via abrazed or welded connection. The bore 40 of the axle receiving bracket38 is sized and configured to receive a bottom bracket axle of thebicycle 10. Attached to the opposed ends of the bottom bracket axle area pair of cranks 42 to which are attached pedals 44. Additionally,attached to one end of the bottom bracket axle between the axlereceiving bracket 38 and a crank 42 is a chainwheel 46 which is adaptedto rotate concurrently with the bottom bracket axle. Rigidly attached toand extending between the head tube 14 and the axle receiving bracket 38is an elongate down tube 48. In the preferred embodiment, the head tube14, top tube 36, axle receiving bracket 38, and down tube 48 each havegenerally cylindrical configurations and are secured to one another viawelded or brazed connections.

Referring now to FIGS. 2 and 3, rigidly attached to the seat tube 16 andtop tube 36 is a cylindrically configured link mount 50 defining a boreextending laterally therethrough. In the preferred embodiment, the linkmount 50 is attached to the seat tube 16 and top tube 36 via a weldingor brazing process. Though the link mount 50 is preferably attached toboth the seat tube 16 and top tube 36 to provide the resultant bicycleframe 12 with greater structural integrity, it will be recognized thatthe link mount 50 may be attached solely to either the seat tube 16 ortop tube 36.

Pivotally connected to the link mount 50 is an upper link 52. In thepreferred embodiment, the upper link 52 defines a front pair of mountingears 54, a back pair of mounting ears 56, and a central pair of mountingears 58. Extending laterally through each pair of mounting ears 54, 56,58 is a pair of coaxially aligned apertures. The upper link 52 ispivotally connected to the link mount 50 by initially orienting thefront pair of mounting ears 54 adjacent the opposed ends of the linkmount 50, i.e. inserting the link mount 50 into the space definedbetween the front pair of mounting ears 54. In this respect, thedistance separating the mounting ears 54 of the front pair is adapted toslidably accommodate the link mount 50. When the link mount 50 isproperly positioned between the front pair of mounting ears 54, the pairof apertures disposed within the mounting ears 54 will be coaxiallyaligned with the bore of the link mount 50. Thereafter, a fastener 60 isinserted into the coaxially aligned apertures and bore thus pivotallyconnecting the upper link 52 to the link mount 50.

The bicycle frame 12 of the present invention further comprises a pairof identically configured seat stay members 62 which have upper endsrigidly attached to an elongate seat stay end housing 64 via a weldingor brazing process. The seat stay end housing 64 defines a boreextending laterally therethrough, and is pivotally connected to theupper link 52. In this respect, the seat stay end housing 64 is insertedinto the space defined between the back pair of mounting ears 56 whichare spaced from each other a distance sufficient to allow the seat stayend housing 64 to be slidably received therebetween. The end housing 64is oriented between the back pair of mounting ears 56 such that theapertures of the mounting ears 56 are coaxially aligned with the bore ofthe end housing 64. Thereafter, a fastener 66 is extended through thecoaxially aligned apertures and bore, thus pivotally securing the endhousing 64, and hence the seat stay members 62, to the upper link 52.Rigidly attached to the lower ends of the seat stay members 62 is a pairof rear wheel axle receiving members 68, one of which is adapted toaccommodate a rear derailleur. The rear wheel axle receiving members 68are adapted to support the rear wheel axle 70 of the rear wheel 72therebetween. Attached to one end of the rear wheel axle 70 is a rearsprocket which is cooperatively engaged to the chainwheel 46 via a chain74.

As best seen in FIGS. 2 and 3, the upper portions of the seat staymembers 62 are arcuately contoured, and bowed inwardly toward the seattube 16 when the end housing 64 is pivotally connected to the upper link52. Rigidly attached to the arcuately contoured portions of the seatstay members 62 in opposed relation is a pair of identically configuredshock mounts 76 which are also directed inwardly toward the seat tube16. In the preferred embodiment, the attachment of the shock mounts 76and rear wheel axle receiving members 68 to the seat stay members 62 isfacilitated by a welding or brazing process.

In addition to the seat stay members 62, the bicycle frame 12 furtherincludes a pair of chain stay members 78 which have front ends rigidlyattached to a chain stay end housing 80 via a welding or brazingprocess. The chain stay end housing 80 defines a pair of mounting ears82 which include a pair of coaxially aligned apertures extendinglaterally therethrough. Disposed within the lower portion of the seattube 16 is a chain stay pivot mount 83 which is extended through acomplimentary aperture extending laterally through the lower portion ofthe seat tube 16 and rigidly secured therewithin via a welding orbrazing process. The mounting ears 82 of the chain stay end housing 80are separated from each other a distance sufficient to allow the opposedends of the chain stay pivot mount 83 to be inserted into the spacedefined between the mounting ears 82. The end housing 80, and moreparticularly the mounting ears 82, are preferably extended about thechain stay pivot mount 83 such that the apertures extending through themounting ears 82 are coaxially aligned with an aperture extendinglaterally through the chain stay pivot mount 83. Thereafter, a fastener84 is extended through the coaxially aligned apertures, thus pivotallyconnecting the end housing 80, and hence the chain stay members 78, tothe chain stay pivot mount 83. Rigidly attached to the back ends of thechain stay members 78 via a welding or brazing process is a pair ofidentically configured clevis members 86, each of which include a pairof juxtaposed end portions 88 having a pair of coaxially alignedapertures extending laterally therethrough.

In the preferred embodiment, the rear wheel axle receiving members 68attached to the lower ends of the seat stay members 62 are pivotallyconnected to the clevis members 86 attached to the back ends of thechain stay members 78. In particular, the frontal portion of each rearwheel axle receiving member 68 is inserted into the space definedbetween the end portions 88 of a respective clevis member 86. In thisrespect, the end portions 88 of each clevis member 86 are separated fromeach other a distance sufficient to allow the frontal portion of therear wheel axle receiving member 68 to be slidably insertedtherebetween. The frontal portion of the rear wheel axle receivingmember 68 is oriented within the clevis member 86 such that an aperturedisposed therein is coaxially aligned with the pair of aperturesextending laterally through the end portions 88 of the clevis member 86.Thereafter, fasteners such as pivot pins 90 are extended through thecoaxially aligned apertures of the end portions 88 and rear wheel axlereceiving members 68, thus pivotally connecting the rear wheel axlereceiving members 68 to the clevis members 86, and hence the chain staymembers 78.

Referring now to FIGS. 2-4, one of the primary components of the bicycleframe 12 is a shock absorber 92. In the preferred embodiment, the shockabsorber 92 comprises a tubular body portion 94 having a reciprocallymovable piston rod 96 extending axially from its bottom end, and anupper coupling section 98 attached to its top end. As best seen in FIG.4, the outer surface of the body portion 94 is threaded so as to allowan upper spring retention member 100 to be threadably received onto thebody portion 94. Rigidly attached to the distal end of the piston rod 96is a lower spring retention member 102 which includes a lower couplingsection 104 formed on the outer surface thereof.

The shock absorber 92 further comprises a helical spring member 106disposed between the upper and lower spring retention members 100, 102in a manner wherein the upper end of the spring member 106 abuts theinner surface of the upper spring retention member 100, the lower end ofthe spring member 106 abuts the inner surface of the lower springretention member 102, and the piston rod 96 of the shock absorber 92extends axially through the center of the spring member 106. As will berecognized, the tension of the spring member 106, and thus the forceneeded to reciprocate the piston rod 96, is adjustable via the selectiveplacement of the upper spring retention member 100 on the threaded outersurface of the body portion 94. Additionally, the shock absorber 92, andin particular the body portion 94 thereof, is preferably fluid-filled,with a suitable fluid being infused thereinto via an inlet-outlet valve108 fluidly coupled to the upper coupling section 98. An elastomerbushing 99 of sufficient resiliency is disposed about the piston rod 96and attached to the inner surface of the lower spring retention member102 to serve as a bump-stop for preventing metal-to-metal contact in theevent the shock absorber 92 "bottoms-out".

As best seen in FIG. 2, the upper coupling section 98 of the shockabsorber 92 is pivotally connected to the upper link 52. In thisrespect, the upper coupling section 98 is sized so as to be slidablyreceivable into the space defined between the central pair of mountingears 58 of the upper link 52. When the upper coupling section 98 isproperly oriented between the mounting ears 58, the pair of aperturesdisposed within the mounting ears 58 are coaxially aligned with anaperture 110 extending laterally through the upper coupling section 98.Thereafter, a fastener such as a pivot pin 112 is extended through thecoaxially aligned mounting ear apertures and aperture 110, thuspivotally connecting the shock absorber 92 to the upper link 52. Inaddition to the pivotal connection of the upper coupling section 98 tothe upper link 52, the lower coupling section 104, and hence the pistonrod 96, is pivotally connected to the seat stay members 62. Inparticular, the lower coupling section 104 is positioned within thespace defined between the shock mounts 76 rigidly attached to the seatstay members 92, and oriented such that the pair of apertures extendinglaterally through the shock mounts 76 are coaxially aligned with anaperture 114 extending laterally through the lower coupling section 104.Thereafter, a fastener such as a pivot pin 116 is extended through thecoaxially aligned shock mount apertures and aperture 114, thus pivotallyconnecting the piston rod 96 to the seat stay members 62. Though notshown, it will be recognized that the shock absorber 92 may be mountedbetween the upper link 52 and seat stay members 62 in a reverseorientation, with the lower coupling section 104 being positionedbetween and pivotally connected to the mounting ears 58 and the uppercoupling section 98 being positioned between and pivotally connected tothe shock mounts 76.

In the present invention, the bicycle frame 12 constructed in thepreviously described manner essentially comprises a four bar linkagesystem. In this respect, the main front triangle portion of the bicycleframe 12 comprising the head tube 14, seat tube 16, top tube 36, axlereceiving bracket 38 and down tube 48 defines the first link of thesystem (i.e. the ground link of the four bar linkage system), while thechain stay members 78 define the second link of the system. The seatstay members 62 define the third link of the system, while the upperlink 52 defines the fourth and final link of the four bar linkagesystem. As such, the shock absorber 92 "floats" since it is pivotallymounted to and extends between the third and fourth links of the linkagesystem, i.e. the seat stay members 62 and upper link 52, and is notrigidly mounted to the first link or ground link of the linkage system,i.e. the main front triangle portion of the bicycle frame 12.

As previously discussed, in the majority of prior art bicycle rearsuspension linkage systems, the shock absorber is mounted directly tothe main front triangle portion of the bicycle frame, thus causing ashock force applied to the rear wheel of the bicycle to be transmitteddirectly to the main front triangle portion as a bending moment ortorque. The transmission of bending moments or torque to the main fronttriangle portion results in a less smooth ride over bumps or uneventerrain. In the present bicycle frame 12, the isolation of the shockabsorber 92 from the main front triangle portion of the bicycle frame 12and the pivotal connection of the upper link 52 and chain stay members78 to the main front triangle portion eliminates the direct transmissionof bending moments or torque to the main front triangle portion when therear wheel 72 encounters bumps or other obstructions, thus enhancing thesmoothness of the ride and the overall performance of the bicycle 10.

As also previously specified, in most prior art rear suspension linkagesystems, the rear axle of the rear wheel pivots about a single elevatedpivot point which typically causes the rear wheel axle to move arcuatelyrather than vertically in a substantially linear fashion. If the rearwheel axle moves in an arc, efficiency is lost due to suspensionoscillations caused by changes in the bicycle wheelbase. Importantly,the various components comprising the bicycle frame 12 of the presentinvention are adapted to provide a suspension for the rear wheel 72 ofthe bicycle 10 which allows the rear wheel axle 70 to move vertically ina substantially linear fashion when the rear wheel 72 encounters a bumpor other obstruction. Additionally, the four bar linkage system definedby the bicycle frame 12 causes the rear wheel axle 70 to be pivotedrelative an instantaneous center of zero velocity or rotation, thelocation of which is optimized to balance the weight transfer (due toforward acceleration), with the chain force pulling the rear wheel axle70 in a downward direction. When the weight transfer forces arebalanced, the bicycle frame 12 is not influenced by pedaling forces.

Referring now to FIGS. 5 and 6, when a shock force is applied to therear wheel 72 of the bicycle 10, the rear wheel axle receiving members68 are moved upwardly in the direction A, which results in the planarmotion of the seat stay members 62 upwardly generally in the directionB. The upward planar motion of the seat stay members 62 in turn causesthe upper link 52 to pivot upwardly about the center point of thefastener 60 in the direction C. Importantly, the upward pivotal motionof the upper link 52 in the direction C concurrently with the planarmotion of the seat stay members 62 in the direction B facilitates thecompression of the helical spring member 106 between the upper and lowerspring retention members 100, 102. The movement of the rear wheel axlereceiving members 68 in the direction A also causes the chain staymembers 78 to pivot upwardly about the center point of the fastener 84in the direction D. Advantageously, due to the structure of the rearsuspension linkage system, the concurrent upward pivoting of the upperlink 52 in the direction C, the planar motion of the seat stay members62 in the direction B, and the upward pivotal movement of the chain staymembers 78 in the direction D causes the rear wheel axle receivingmembers 68 and hence the rear wheel axle 70 to move generally verticallyupwardly in the direction A when the rear wheel 72 is subjected to ashock force.

Due to the placement of the shock absorber 92 between the upper link 52and seat stay members 62, the upward pivotal movement of the upper link52, seat stay members 62, rear wheel axle receiving members 68 and chainstay members 78 is controlled and limited thereby. In this respect, theshock absorber 92 is adapted to absorb some of the shock force exertedon the rear wheel 72 as such force is transmitted through the linkageassembly. As will be recognized, the amount of the shock force absorbedby the shock absorber 92 may be selectively adjusted via the positioningof the upper spring retention member 100 along the threaded outersurface of the body portion 94. In particular, the positioning of theupper spring retention member 100 allows the spring preload to beadjusted, thus allowing for adjustments to static ride height, differentrider weights and varying riding conditions.

As previously specified, the mounting of the shock absorber 92 solely tothe third and fourth links of the linkage system, i.e. to the upper link52 and seat stay members 62, also eliminates the transmission of theshock force as bending moments to the main front triangle portion of thebicycle frame 12, thus enhancing the overall performance characteristicsof the bicycle 10. In addition to the foregoing, this particularplacement of the shock absorber 92 serves to reinforce the primaryin-line pivot of the four bar linkage system, i.e. the pivot pointdefined by the attachment of the seat stay end housing 64 to the upperlink 52 via the fastener 66. Since, in most prior art rear suspensionlinkage systems, the primary pivot point of the linkage system is notreinforced by the shock absorber, the linkage system is more susceptibleto mechanical failure.

Due to the structure of the bicycle frame 12, the ratio of movement,i.e. the motion ratio, between the rear wheel axle 70 in the direction Aand the helical spring member 106 as it is being compressed is constantthroughout the range of travel of the rear wheel axle 70, thus providinga relatively flat wheel rate when the rear wheel 72 encounters a shockor other obstruction. As previously discussed, this flat wheel rate ismore desirable than a regressive or progressive wheel rate wherein theshock travel and rear wheel axle travel are disproportionate.

Additional modifications and improvements of the present invention mayalso be apparent to those skilled in the art. Thus, the particularcombination of parts described and illustrated herein is intended torepresent only one embodiment of the invention, and is not intended toserve as limitations of alternative devices within the spirit and scopeof the invention.

What is claimed is:
 1. A bicycle rear suspension linkage system,comprising:a bicycle frame; an upper link having front and back ends anda central portion, the front end of said upper link being pivotallyconnected to said bicycle frame; a pair of seat stay members havingupper and lower ends, the upper ends of said seat stay members beingpivotally connected to the back end of said upper link; a pair of chainstay members having front and back ends, the front ends of said chainstay members being pivotally connected to said bicycle frame and theback ends of said chain stay members being pivotally connected to thelower ends of said seat stay members; and a shock absorber having a bodyportion and a reciprocally movable piston rod extending axially fromsaid body portion, said piston rod defining a distal end pivotallyconnected to said seat stay members and said body portion beingpivotally connected to the central portion of said upper link.
 2. Thelinkage system of claim 1 wherein said shock absorber further comprisesa spring member extending between said body portion and said seat staymembers, said piston rod extending axially through said spring member.3. The linkage system of claim 1 wherein said bicycle frame comprises:ahead tube disposed at the front of the bicycle frame; a seat tubedisposed at the rear of the bicycle frame; and an elongate top tubehaving opposed ends rigidly attached to said head tube and said seattube.
 4. The linkage system of claim 3 wherein the front end of saidupper link is pivotally connected to said top tube.
 5. The linkagesystem of claim 3 wherein the front end of said upper link is pivotallyconnected to said seat tube.
 6. The linkage system of claim 3 whereinsaid bicycle frame further comprises a link mount rigidly attached tosaid top tube, the front end of said upper link being pivotallyconnected to said link mount.
 7. The linkage system of claim 3 whereinsaid bicycle frame further comprises a link mount rigidly attached tosaid seat tube, the front end of said upper link being pivotallyconnected to said link mount.
 8. The linkage system of claim 3 whereinsaid bicycle frame further comprises a link mount rigidly attached tosaid seat tube and said top tube, the front end of said upper link beingpivotally connected to said link mount.
 9. The linkage system of claim 3wherein the front ends of said chain stay members are pivotallyconnected to said seat tube.
 10. The linkage system of claim 3 whereinsaid bicycle frame further comprises a chain stay pivot mount rigidlyattached to said seat tube, the front ends of said chain stay membersbeing pivotally connected to said chain stay pivot mount.
 11. Thelinkage system of claim 3 wherein the front ends of said chain staymembers are rigidly attached to a chain stay end housing, said chainstay end housing being pivotally connected to said seat tube.
 12. Thelinkage system of claim 11 wherein said bicycle frame further comprisesa chain stay pivot mount rigidly attached to said seat tube, said chainstay end housing being pivotally connected to said chain stay pivotmount.
 13. The linkage system of claim 1 wherein the front ends of saidchain stay members are rigidly attached to a chain stay end housing,said chain stay end housing being pivotally connected to said bicycleframe.
 14. The linkage system of claim 1 wherein the upper ends of saidseat stay members are rigidly attached to a seat stay end housing, saidseat stay end housing being pivotally connected to the back end of saidupper link.
 15. A bicycle rear suspension linkage system, comprising:abicycle frame including a head tube, a seat tube and an elongate toptube having opposed ends rigidly attached to said head tube and saidseat tube; an upper link pivotally connected to the top tube of saidbicycle frame; a pair of seat stay members having upper and lower ends,said upper ends being pivotally connected to said upper link; a pair ofchain stay members having front and back ends, said front ends beingpivotally connected to said bicycle frame and said back ends beingpivotally connected to the lower ends of said seat stay members; and ashock absorber having a body portion and a reciprocally movable pistonrod extending axially from said body portion, said piston rod defining adistal end pivotally connected to said seat stay members and said bodyportion being pivotally connected to said upper link.
 16. A bicycle rearsuspension linkage system, comprising:a bicycle frame including a headtube, a seat tube, an elongate top tube having opposed ends rigidlyattached to said head tube and said seat tube, and a link mount rigidlyattached to said top tube; an upper link pivotally connected to saidlink mount; a pair of seat stay members having upper and lower ends,said upper ends being pivotally connected to said upper link; a pair ofchain stay members having front and back ends, said front ends beingpivotally connected to said bicycle frame and said back ends beingpivotally connected to the lower ends of said seat stay members; and ashock absorber having a body portion and a reciprocally movable pistonrod extending axially from said body portion, said piston rod defining adistal end pivotally connected to said seat stay members and said bodyportion being pivotally connected to said upper link.
 17. A bicycle rearsuspension linkage system, comprising:a bicycle frame including a headtube, a seat tube, an elongate top tube having opposed ends rigidlyattached to said head tube and said seat tube, and a link mount rigidlyattached to said seat tube and said top tube; an upper link pivotallyconnected to said link mount; a pair of seat stay members having upperand lower ends, said upper ends being pivotally connected to said upperlink; a pair of chain stay members having front and back ends, saidfront ends being pivotally connected to said bicycle frame and said backends being pivotally connected to the lower ends of said seat staymembers; and a shock absorber having a body portion and a reciprocallymovable piston rod extending axially from said body portion, said pistonrod defining a distal end pivotally connected to said seat stay membersand said body portion being pivotally connected to said upper link.